1. Field of the Invention
The present invention relates to an audio amplifier, and particularly, to a so-called tube amplifier using vacuum tubes.
2. Description of the Prior Art
Various tube amplifiers have conventionally been proposed. Most of those amplifiers use a capacitor for connecting stages to each other. Specifically, in order that a positive high voltage applied to a plate (anode) of a vacuum tube in a preceding stage is not applied to a grid of a vacuum tube in a succeeding stage, a capacitor of about 0.05 .mu.F is inserted between the plate of the vacuum tube in the preceding stage and the grid of the succeeding stage, and a signal is transmitted from the preceding stage to the succeeding stage through the capacitor.
In addition, am amplifier using no capacitor between stages is known as a kind of direct-current amplifier or the like, but is not suitable for power-amplification of an audio signal.